i) Field of the Invention
This invention relates to a composition for forming a repulpable, water resistant, grease resistant, water vapor permeable coating on a porous paper sheet material; a repulpable coated paperboard liner for use in corrugated paperboard packaging manufacture, a method of producing a repulpable coated paperboard liner; a repulpable corrugated paperboard and a method of producing a repulpable corrugated paperboard.
ii) Description of Prior Art
Perishable food products such as frozen meat, fish and vegetables are shipped, stored and displayed for sale in packages formed of corrugated paperboard coated with a water resistant or repellant material, the most widely used coating being a wax coating. The wax coating renders the packages resistant or repellant to water and impermeable to water vapor.
Such packages, however, have a serious disadvantage in that they are essentially non-repulpable. Repulping refers to the art of recycling waste paper products including paperboard to provide a reusable wood pulp. Recyclability of waste paper products is of growing importance in efficiently employing available wood fibre resources and in curtailing the amount of waste which is either combusted or disposed of in landfill sites.
The problem in recycling wax-coated paperboard is well established and is described in, for example, U.S. Pat. Nos. 5,626,945 and 5,562,980 and PCT International Publication WO 96/22329.
An additional problem or manufacturing limitation with existing water repellent coatings, such as wax coatings, for corrugated paperboard packaging, is that the wax coating can only be applied to the finished or assembled corrugated paperboard.
Corrugated paperboard comprises an assembly of a pair of spaced apart linerboards with a corrugated medium sandwiched therebetween and adhered thereto. In particular, the tips of the flutes of the corrugated medium are adhered by an adhesive to the inwardly facing surfaces of the linerboards. The most widely used adhesives are aqueous starch-based adhesives which meet Government standards, e.g., FDA standards, for food packages. After assembly the adhesive is dried liberating water vapor which escapes through the porous uncoated linerboards.
If the wax coating were to be applied to the linerboards prior to assembly of the corrugated paperboard, the vapor impermeable wax coating would prevent the escape of the water vapor from the adhesive and the water vapor would be trapped and condense in the interior of the corrugated paperboard.
Consequently employing conventional water vapor impermeable coatings such as the wax coatings, necessitates complete assembly and formation of the corrugated paperboard before application of the vapor impermeable coating. This places significant restrictions on the manufacturing process.